Light-Emitting Element, Display Module, Lighting Module, Light-Emitting Device, Display Device, Electronic Device, and Lighting Device

ABSTRACT

A tandem light-emitting element in which generation of crosstalk can be suppressed even when the element is applied to a high-definition display is provided. In the tandem light-emitting element, a layer in contact the anode side of an intermediate layer contains 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. In particular, oneembodiment of the present invention relates to a semiconductor device, adisplay device, a light-emitting device, a driving method thereof, or amanufacturing method thereof. In particular, one embodiment of thepresent invention relates to a light-emitting element which includes alight-emitting layer containing an organic compound between a pair ofelectrodes. Furthermore, the present invention relates to alight-emitting device including the light-emitting element and anelectronic device including the light-emitting device.

2. Description of the Related Art

In recent years, mobile devices show remarkable development, and one caneasily enjoy image works anytime and anywhere with a small imagereproducing device, a display of a smartphone or a tablet terminal, andthe like. In addition, image data is being more often downloaded ortransferred by using a small memory, and thus, the demand for the mobiledevices is being increased.

In order to enjoy high-quality images with a small display such as adisplay of a mobile device, the display is required to have sufficientlyhigh definition.

A light-emitting element (also referred to as an electroluminescenceelement or an EL element) which includes a light-emitting layercontaining an organic compound between a pair of electrodes is capableof high-speed response and DC drive at low voltage, and can bemanufactured to be thin and lightweight. Therefore, the light-emittingelement is being put into practical use as a flat panel display elementor a mobile display element.

An EL element includes a pair of electrodes and an EL layer containing alight-emitting substance, which is provided between the electrodes, andemits light when the light-emitting substance contained in the EL layeris excited by current flowing through the EL layer. Therefore, in orderto obtain high emission intensity in such an EL element, currentcorresponding to the intensity needs to flow through the light-emittinglayer, and power consumption is increased accordingly. In addition, aslarge current flows, degradation of the EL element is accelerated.

In view of the above, a light-emitting element which includes a stack ofa plurality of EL layers and thereby capable of emitting light withhigher luminance than a light-emitting element including only one ELlayer, when current having the same current density flows through eachlight-emitting element, is proposed (e.g., see Patent Document 1). In alight-emitting element disclosed in Patent Document 1, a plurality oflight-emitting units is separated from each other by a charge generationlayer.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2003-272860

SUMMARY OF THE INVENTION

In the case of manufacturing a high-definition display by using alight-emitting element (hereinafter referred to as a tandemlight-emitting element) as disclosed in Patent Document 1 in which aplurality of light-emitting units is separated from each other by acharge generation layer, problems which do not arise in lightingapplication or a display having a large pixel size are caused in somecases. One of such problems is an interference phenomenon betweenadjacent pixels, that is, crosstalk.

In the case of manufacturing a display by using a tandem light-emittingelement, since white light emission can be easily obtained, such afull-color display is fabricated in many cases in which the same ELlayer structure is employed for all pixels and a resonant structureand/or a color filter is combined so that each pixel can emit light ofits expected color. That is, the EL layer is continuous between adjacentpixels.

In addition, a light-emitting element includes the EL layer between apair of electrodes. In an active matrix light-emitting element, one ofthe pair of electrodes is divided for each pixel but the other electrodeis continuous between a plurality of pixels. Accordingly, the pixel isdriven by controlling the electrode divided for each pixel.

When part of the EL layer that is continuous between a plurality oflight-emitting elements has high conductivity, in some cases, currentalso flows between a first electrode of an element which is to bedriven, and an electrode (second electrode) that is continuous andprovided in the adjacent pixel, leading to crosstalk. Part of the ELlayer which has high conductivity is formed owing to a charge generationlayer, which has therefore attracted attention.

In the charge generation layer, in order to improve anelectron-injection property to a light-emitting unit on the anode side,an alkali metal such as lithium or cesium is used. In addition, anelectron-transport material such as bathocuproine (abbreviation: BCP) orbathophenanthroline (abbreviation: BPhen) is widely used because, withthese materials, a light-emitting element with low drive voltage andfavorable characteristics can be manufactured. However, when the alkalimetal is dispersed, the conductivity is increased, which leads tocrosstalk in a high-definition display. Furthermore, it was found thateven when the alkali metal and the electron-transport material are notmixed and only in contact with each other, crosstalk is similarlycaused.

Without the alkali metal, the electron-injection property to thelight-emitting unit deteriorates, and the drive voltage is increased. Inthis manner, it is very difficult to suppress crosstalk of the tandemlight-emitting element while keeping sufficient characteristics forpractical use.

Furthermore, it is known that a light-emitting element containing theabove-described phenanthroline-based electron-transport material withfavorable drive characteristics, such as bathocuproine (abbreviation:BCP) or bathophenanthroline (abbreviation: BPhen), has low heatresistance. Low heat resistance is a big problem for the elementdepending on the element structure.

In view of the above, it is an object of one embodiment of the presentinvention to provide a tandem light-emitting element in which generationof crosstalk can be suppressed even when the element is applied to ahigh-definition display.

It is another object of one embodiment of the present invention toprovide a tandem light-emitting element which can display high-qualityimages.

It is another object of one embodiment of the present invention toprovide a light-emitting element which can display high-quality imagesand consumes low power.

It is another object of one embodiment of the present invention toprovide a tandem light-emitting element with high heat resistance. It isanother object of one embodiment of the present invention to provide anovel light-emitting element.

It is another object of one embodiment of the present invention toprovide, by using the above light-emitting element, a display module, alighting module, a light-emitting device, a display device, anelectronic device, and a lighting device which can display high-qualityimages.

It is another object of one embodiment of the present invention toprovide, by using the above light-emitting element, a display module, alighting module, a light-emitting device, a display device, anelectronic device, and a lighting device which can display high-qualityimages and consume low power.

It is another object of one embodiment of the present invention toprovide, by using the above light-emitting element, a display module, alighting module, a light-emitting device, a display device, anelectronic device, and a lighting device which have high heatresistance.

It is only necessary that at least one of the above-described objects beachieved in the present invention.

The above-described objects can be achieved with a tandem light-emittingelement containing2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBPhen) in a layer in contact with the anode side of an intermediatelayer.

One embodiment of the present invention is a light-emitting elementincluding a first electrode, a second electrode, and an EL layer betweenthe first electrode and the second electrode. The EL layer includes atleast a plurality of light-emitting units and a plurality of chargegeneration layers each provided between the light-emitting units. Alayer in contact with the anode side of the charge generation layercontains NBPhen.

Another embodiment of the present invention is a light-emitting elementincluding a first electrode, a second electrode, and an EL layer betweenthe first electrode and the second electrode. The EL layer includes afirst light-emitting unit provided on the anode side and a secondlight-emitting unit provided on the cathode side. A charge generationlayer is provided between the first light-emitting unit and the secondlight-emitting unit. A layer in contact with the charge generation layerof the first light-emitting unit contains NBPhen.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the charge generation layer includesat least a charge generation region and an electron-injection bufferregion. The electron-injection buffer region is provided on the anodeside of the charge generation layer.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which an electron-relay region is providedon the charge generation region side of the electron-injection bufferregion.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the electron-injection buffer regioncontains an alkali metal.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the alkali metal is lithium.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the EL layer includes at least alayer containing a condensed aromatic compound or a condensedheteroaromatic compound and a layer which is in contact with the layercontaining a condensed aromatic compound or a condensed heteroaromaticcompound and contains NBPhen.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the EL layer includes at least alayer containing a condensed aromatic compound or a condensedheteroaromatic compound having three or more condensed rings and a layerwhich is in contact with the layer containing a condensed aromaticcompound or a condensed heteroaromatic compound and contains NBPhen.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the layer containing a condensedaromatic compound or a condensed heteroaromatic compound is a layercontaining a condensed heteroaromatic compound.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which a condensed heteroaromatic compoundin the layer containing a condensed heteroaromatic compound includes twonitrogen atoms in one condensed ring.

Another embodiment of the present invention is a light-emitting elementwith the above structure, which emits phosphorescence.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the layer containing a condensedheteroaromatic compound further contains iridium.

Another embodiment of the present invention is a light-emitting elementwith the above structure, in which the iridium is contained in part ofthe layer containing a condensed heteroaromatic compound and is notcontained in a region in contact with the layer containing NBPhen.

One embodiment of the present invention is a display module includingany of the above light-emitting elements.

One embodiment of the present invention is a lighting module includingany of the above light-emitting elements.

One embodiment of the present invention is a light-emitting deviceincluding any of the above light-emitting elements and a unit forcontrolling the light-emitting element.

One embodiment of the present invention is a display device includingany of the above light-emitting elements in a display portion and a unitfor controlling the light-emitting element.

One embodiment of the present invention is a lighting device includingany of the above light-emitting elements in a lighting portion and aunit for controlling the light-emitting element.

One embodiment of the present invention is an electronic deviceincluding any of the above light-emitting elements.

Note that the light-emitting device in this specification includes animage display device including a light-emitting element. Further, thecategory of the light-emitting device in this specification includes amodule in which a light-emitting element is provided with a connectorsuch as an anisotropic conductive film or a tape carrier package (TCP);a module in which the end of the TCP is provided with a printed wiringboard; and a module in which an IC (integrated circuit) is directlymounted on a light-emitting element by a COG (chip on glass) method. Thelight-emitting device also includes the one used in lighting equipmentand the like.

According to one embodiment of the present invention, a tandemlight-emitting element can be provided, in which generation of crosstalkcan be suppressed even when the element is applied to a high-definitiondisplay.

According to one embodiment of the present invention, a tandemlight-emitting element can be provided, which can display high-qualityimages.

According to one embodiment of the present invention, a light-emittingelement can be provided, which can display high-quality images andconsumes low power.

According to one embodiment of the present invention, a tandemlight-emitting element with high heat resistance can be provided.

According to one embodiment of the present invention, by using the abovelight-emitting element, a display module, a lighting module, alight-emitting device, a display device, an electronic device, and alighting device each of which can display high-quality images can beprovided.

According to one embodiment of the present invention, by using the abovelight-emitting element, a display module, a lighting module, alight-emitting device, a display device, an electronic device, and alighting device each of which can display high-quality images andconsumes low power can be provided.

According to one embodiment of the present invention, by using the abovelight-emitting element, a display module, a lighting module, alight-emitting device, a display device, an electronic device, and alighting device which have high heat resistance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of a light-emitting element.

FIGS. 2A and 2B are conceptual diagrams of an active matrixlight-emitting device.

FIGS. 3A and 3B are conceptual diagrams of active matrix light-emittingdevices.

FIG. 4 is a conceptual diagram of an active matrix light-emittingdevice.

FIGS. 5A to 5D each illustrate an electronic device.

FIG. 6 illustrates in-vehicle display devices and lighting devices.

FIGS. 7A to 7C illustrate an electronic device.

FIG. 8 shows current density-luminance characteristics of an exampleelement 1 and a comparative example element 1.

FIG. 9 shows luminance-current efficiency characteristics of the exampleelement 1 and the comparative example element 1.

FIG. 10 shows voltage-luminance characteristics of the example element 1and the comparative example element 1.

FIG. 11 shows emission spectra of the example element 1 and thecomparative example element 1.

FIG. 12 shows enlarged photographs of display devices in which anexample element 2 and a comparative element 2 are used.

FIG. 13 illustrates an element structure of a light-emitting element.

FIG. 14 shows time dependence characteristics of normalized luminance ofthe example element 1.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings. However, the present invention isnot limited to the following description and it is easily understood bythose skilled in the art that the mode and details can be variouslychanged without departing from the scope and spirit of the presentinvention. Accordingly, the present invention should not be interpretedas being limited to the content of the embodiments below.

Embodiment 1

FIG. 1 is a conceptual diagram of a light-emitting element according toone embodiment of the present invention. The light-emitting elementillustrated in FIG. 1 includes a plurality of (n) light-emitting unitsbetween a pair of electrodes (an anode 100 and a cathode 101). Thelight-emitting unit which is the closest to the anode 100 is a firstlight-emitting unit 102 k, and the light-emitting unit which is theclosest to the cathode 101 is an n-th light-emitting unit 102 n.

The light-emitting element illustrated in FIG. 1 includes thelight-emitting units (the first light-emitting unit 102 k . . . an m-thlight-emitting unit 102 m . . . the n-th light-emitting unit 102 n);charge generation layers (a first charge generation layer 103 k . . . anm-th charge generation layer 103 m . . . an (n−1)-th charge generationlayer 103 n−1); charge generation regions (a first charge generationregion 104 k . . . an m-th charge generation region 104 m . . . an(n−1)-th charge generation region 104 n−1); electron-injection bufferregions (a first electron-injection buffer region 105 k . . . an m-thelectron-injection buffer region 105 m . . . an (n−1)-thelectron-injection buffer region 105 n−1); layers containing NBPhen (afirst layer 106 k containing NBPhen . . . an m-th layer 106 m containingNBPhen . . . an (n−1)-th layer 106 n−1 containing NBPhen . . . an n-thlayer 106 n containing NBPhen); and the like.

In some cases, a plurality of light-emitting units, a plurality ofcharge generation layers, a plurality of charge generation regions, aplurality of electron-injection buffer regions, and a plurality oflayers containing NBPhen are collectively referred to as alight-emitting unit 102, a charge generation layer 103, a chargegeneration region 104, an electron-injection buffer region 105, and alayer 106 containing NBPhen, respectively. In addition, thelight-emitting units 102 between the anode 100 and the cathode 101 andthe charge generation layers 103 each provided between thelight-emitting units are collectively referred to as an EL layer 110.

The m-th charge generation layer 103 m (m is a natural number, 1≦m≦n−1)is provided between and in contact with the m-th light-emitting unit 102m and an (m+1)-th light-emitting unit 102 m+1. The m-th chargegeneration layer 103 m includes the m-th charge generation region 104 min contact with the (m+1)-th light-emitting unit 102 m+1 and the m-thelectron-injection buffer region 105 m in contact with the m-th chargegeneration region 104 m and the m-th light-emitting unit 102 m. Here,the charge generation layer 103 is in a floating state in which a powersource or the like is not connected to the charge generation layer 103.In addition, the charge generation region 104 contains a substancehaving a hole-transport property and an acceptor substance with respectto the substance having a hole-transport property. Theelectron-injection buffer region 105 is a layer which has functions ofaccepting electrons generated in the charge generation region 104 anddonating the electrons to the layer 106 containing NBPhen of thelight-emitting unit 102.

The electron-injection buffer region 105 includes at least a very thinlayer formed of an alkali metal, particularly, lithium, having athickness of 0.1 nm to 5 nm at the interface on the anode side. Sincethe very thin layer is provided, an injection barrier of electrons isrelieved, whereby electrons generated in the charge generation region104 can be smoothly injected to the light-emitting unit 102. Inaddition, in the electron-injection buffer region 105, an electron-relayregion may be provided between the lithium layer and the chargegeneration region 104 to prevent the interaction between the lithiumlayer and the charge generation region 104. The electron-relay regionalso functions as a layer for efficiently injecting electrons generatedin the charge generation region 104 to the light-emitting unit 102.Thus, the electron-relay region may be formed so that the LUMO level ofthe electron-relay region can be a level between the acceptor level ofthe acceptor substance in the charge generation region 104 and the LUMOlevel of the layer in contact with the anode side of the chargegeneration layer 103 in which the electron-relay region is included(that is, the layer 106 containing NBPhen). Specifically, the LUMO levelof the electron-relay region is preferably approximately higher than orequal to −5.0 eV and lower than or equal to −3.0 eV. The electron-relayregion may be formed to a thickness of 1 nm to 40 nm, preferably, 1 nmto 10 nm.

Furthermore, the light-emitting unit 102 includes a plurality of layerseach containing an organic compound and having a specific function. Asthe plurality of layers, the light-emitting unit 102 includes at least alight-emitting region containing a light-emitting substance and thelayer 106 containing NBPhen, and the nm-th light-emitting unit 102 mincludes the nm-th layer 106 m containing NBPhen. In this embodiment,the layer 106 containing NBPhen is provided to be the closest to thecathode 101 in each of the light-emitting units 102. The m-th layer 106m containing NBPhen included in the nm-th light-emitting unit 102 m isformed so as to be in contact with the m-th electron-injection bufferregion 105 m included in the m-th charge generation layer 103 m.

Although an example in which a large number of light-emitting units areprovided is illustrated in FIG. 1, a light-emitting element whichincludes a smaller number of light-emitting units than the illustratedexample, such as the case where n=2 or 3, is also of course oneembodiment of the present invention. For example, in the case where twolight-emitting units 102 are provided, n=2, and the m-th light-emittingunit 102 m corresponds to the first light-emitting unit 102 k, and the(m+1)-th light-emitting unit 102 m+1 corresponds to the n-thlight-emitting unit 102 n.

The charge generation region 104 contains, as described above, thesubstance having a hole-transport property and the accepter substance.When voltage is applied between the electrodes (the anode 100 and thecathode 101), in the charge generation region 104, the acceptorsubstance extracts electrons from the substance having a hole-transportproperty to generate electrons and holes. The holes generated in them-th charge generation region 104 m are injected to the (m+1)-thlight-emitting unit 102 m+1. The electrons generated in the m-th chargegeneration region 104 m at the same time are injected to the layercontaining NBPhen (the m-th layer 106 m containing NBPhen) of the m-thlight-emitting unit 102 m through the m-th electron-injection bufferregion 105 m. The charge generation region 104 is preferably formed to athickness of greater than or equal to 10 nm and less than or equal to200 nm.

As the acceptor substance contained in the charge generation region 104,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Moreover, oxides of metals belonging toGroups 4 to 8 of the periodic table can be given. Specifically, it ispreferable to use vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide because of their high electron-accepting properties. Inparticular, molybdenum oxide is preferable because of its stability inthe atmosphere, low hygroscopic property, and easiness of handling.

As the substance having a hole-transport property, any of a variety oforganic compounds such as aromatic amine compounds, carbazolederivatives, aromatic hydrocarbons, and high molecular compounds (e.g.,oligomers, dendrimers, or polymers) can be used. Note that a substancehaving a hole mobility of higher than or equal to 10⁻⁶ cm²/Vs ispreferable.

As the aromatic amine compounds, for example, there areN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

As specific examples of the carbazole derivatives, the following can begiven: 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like. Moreover,4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP);1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB);9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA);1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene; and the likecan also be used.

Examples of the aromatic hydrocarbons include2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]-anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Besides, pentacene, coronene, and the like can be used. Thearomatic hydrocarbon which has a hole mobility of higher than or equalto 1×10⁻⁶ cm²/Vs and which has 14 to 42 carbon atoms is particularlypreferable.

The aromatic hydrocarbon may have a vinyl skeleton. As aromatichydrocarbon having a vinyl group, the following are given, for example:4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi);9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA);and the like.

Moreover, high molecular compounds such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](abbreviation:Poly-TPD) can also be used.

Here, as the substance having a hole-transport property, which is usedfor the charge generation region 104, a substance which does not have anamine skeleton is more preferably used. In the case where the chargegeneration region 104 is formed by using the acceptor substance and thesubstance having a hole transport property which does not have an amineskeleton, absorption based on charge transfer interaction is hard tooccur as compared to the case where the substance having ahole-transport property has an amine skeleton. Although absorption basedon charge transfer interaction does not occur, the charge generationregion 104 can sufficiently function as a charge generation region.Hence, the charge generation region 104 which does not have anabsorption peak in the visible light region and functions as a chargegeneration region can easily be formed, whereby a reduction in emissionefficiency due to absorption of light can be prevented.

Note that examples of the substance having a hole-transport propertywhich does not have an amine skeleton include the above-describedcarbazole derivatives such as CBP, TCPB, CzPA,9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene;and aromatic hydrocarbon such as t-BuDNA, DPPA, t-BuDBA, DNA, DPAnth,t-BuAnth, DMNA, 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,DPVBi, and DPVPA. Further, a polymer of a carbazole derivative, such asPVK, may be used.

For the charge generation region 104, a composite material is preferablyused, in which the acceptor substance and the substance having ahole-transport property are contained so that the mass ratio of theacceptor substance to the substance having a hole-transport property isgreater than or equal to 0.1:1 and less than or equal to 4.0:1.

The charge generation region 104 can be formed to a thickness of greaterthan or equal to 10 nm and less than or equal to 200 nm. When the chargegeneration region 104 is formed by using a composite material of thesubstance having a hole-transport property and the acceptor substance, achange in conductivity is small even when the thickness of the chargegeneration region 104 is increased; thus, increase in drive voltage ofthe light-emitting element due to increase in the thickness of thecharge generation region 104 can be suppressed. When the chargegeneration region 104 is formed by using such a material, by adjustingthe thickness of the charge generation region 104, optical adjustment ofthe light-emitting element can be performed without increase in drivevoltage.

The charge generation region 104 is not limited to the structure inwhich one film contains the substance having a hole-transport propertyand the acceptor substance, and can be a stack of a layer containing thesubstance having a hole-transport property and a layer containing theacceptor substance. Note that in the case of a stacked structure, in them-th charge generation region 104 m, a layer containing the substancehaving a hole-transport property is formed in contact with the (m+1)-thlight-emitting unit 102 m+1, and a layer containing the acceptorsubstance is formed in contact with the m-th electron-injection bufferregion 105 m.

In the electron-injection buffer region 105, at least an alkali metallayer is formed in contact with the light-emitting unit 102. As thealkali metal, lithium and a compound of lithium are preferable;specifically, lithium, lithium fluoride, lithium oxide, and the like canbe used. The thickness of the alkali metal layer may be 1 nm to 10 nm inorder to suppress crosstalk. In addition, since the alkali metal layeris very thin, it is not necessarily continuous throughout the pixelportion and may be partly divided into an island shape.

In the electron-injection buffer region 105, an electron-relay regionmay be formed to prevent the interaction between the alkali metal layerand the charge generation region. The electron-relay region is formedbetween the alkali metal layer and the charge generation region and hasfunctions of accepting electrons generated in the charge generationregion 104 and donating the electrons to the layer 106 containing NBPhenof the light-emitting unit 102. In addition, the electron-relay regioncontains at least a substance having an electron-transport property.

Here, the electron-relay region is formed so that the LUMO level of thesubstance having an electron-transport property contained in theelectron-relay region can be a level between the acceptor level of theacceptor substance in the charge generation region 104 and the LUMOlevel of the layer 106 containing NBPhen. As a specific value of theenergy level, the LUMO level of the substance having anelectron-transport property contained in the electron-relay region ispreferably higher than or equal to −5.0 eV, more preferably higher thanor equal to −5.0 eV and lower than or equal to −3.0 eV.

As the substance having an electron-transport property in theelectron-injection buffer region, a phthalocyanine-based material or ametal complex having a metal-oxygen bond and an aromatic ligand ispreferably used.

In the case where a phthalocyanine-based material is used, specifically,any of copper(II) phthalocyanine (abbreviation: CuPc), phthalocyanine(abbreviation: H₂Pc), phthalocyanine tin(II) complex (abbreviation:SnPc), phthalocyanine zinc complex (abbreviation: ZnPc), cobalt(II)phthalocyanine, β-form (abbreviation: CoPc), phthalocyanine iron(abbreviation: FePc), and vanadyl2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (abbreviation: PhO-VOPc)is preferably used.

When a metal complex having a metal-oxygen bond and an aromatic ligandis used, a metal complex having a metal-oxygen double bond ispreferable. In addition, as a metal complex having a metal-oxygen bondand an aromatic ligand, a phthalocyanine-based material is alsopreferable. Specifically, any of vanadyl phthalocyanine (abbreviation:VOPc), a phthalocyanine tin(IV) oxide complex (abbreviation: SnOPc), anda phthalocyanine titanium oxide complex (abbreviation: TiOPc) ispreferable because a metal-oxygen double bond is more likely to act onanother molecule in terms of a molecular structure and an acceptorproperty is high.

Note that the phthalocyanine-based material preferably has a phenoxygroup. Specifically, a phthalocyanine derivative having a phenoxy groupsuch as PhO-VOPc is preferable.

The electron-relay region may further contain a donor substance.Examples of the donor substance include an organic compound such astetrathianaphthacene (abbreviation: TTN), nickelocene, anddecamethylnickelocene, in addition to an alkali metal, an alkaline earthmetal, a rare earth metal, and a compound of the above metals (e.g., analkali metal compound (including an oxide such as lithium oxide, ahalide, and a carbonate such as lithium carbonate or cesium carbonate),an alkaline earth metal compound (including an oxide, a halide, and acarbonate), and a rare earth metal compound (including an oxide, ahalide, and a carbonate)). When such a donor substance is contained inthe electron-relay region, electrons can be transferred easily and thelight-emitting element can be driven at lower voltage.

When a donor substance is contained in the electron-relay region, as thesubstance having an electron-transport property contained in theelectron-relay region, a substance with a LUMO level higher than theacceptor level of the acceptor substance contained in thecharge-generation region can be used, in addition to the above-describedmaterials. As a specific energy level, the LUMO level is higher than orequal to −5.0 eV, preferably higher than or equal to −5.0 eV and lowerthan or equal to −3.0 eV. Examples of such a substance include aperylene derivative and a nitrogen-containing condensed aromaticcompound. Note that a nitrogen-containing condensed aromatic compound ispreferably used for the electron-relay region because of its stability.Furthermore, among nitrogen-containing condensed aromatic compounds, astructure in which a compound having an electron-withdrawing group suchas a cyano group or a fluoro group is used is a preferable structurebecause electrons are easily accepted in the electron-relay region.

As specific examples of the perylene derivative, the following can begiven: 3,4,9,10-perylenetetracarboxylic dianhydride (abbreviation:PTCDA), 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole(abbreviation: PTCBI), N,N′-dioctyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI-C8H),N,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide (abbreviation: HexPTC), and the like.

As specific examples of the nitrogen-containing condensed aromaticcompound, the following can be given:pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation:PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene(abbreviation: HAT(CN)₆), 2,3-diphenylpyrido[2,3-b]pyrazine(abbreviation: 2PYPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine(abbreviation: F2PYPR), and the like.

Besides, 7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ),1,4,5,8-naphthalenetetracarboxylic dianhydride (abbreviation: NTCDA),perfluoropentacene, copper hexadecafluorophthalocyanine (abbreviation:F₁₆CuPc),N,N′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylic diimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene(abbreviation: DCMT), methanofullerenes (e.g., [6,6]-phenyl C₆₁ butyricacid methyl ester), and the like can be used.

In the case where a donor substance is contained in the electron-relayregion, the electron-injection buffer region may be formed by a methodsuch as co-evaporation of the substance having an electron-transportproperty and the donor substance. In the case where the donor substanceis contained, the electron-relay region is preferably formed to athickness of 1 nm to 10 nm, in which case generation of crosstalk due tothe electron-relay region can be suppressed. For the same reason, theelectron-relay region preferably contains the donor substance so thatthe mass ratio of the donor substance to the substance having anelectron-transport property is greater than or equal to 0.001:1 and lessthan or equal to 0.1:1.

Each of the light-emitting units is formed by stacking a plurality oflayers each having a different function, and includes at least alight-emitting layer (not illustrated) containing a light-emittingsubstance and the layer containing NBPhen.

The layer 106 containing NBPhen functions as part of anelectron-transport layer and is in contact with the electron-injectionbuffer region 105. With this structure, interference in the adjacentpixel can be effectively reduced even in a high-definition display.

The electron-transport layer includes the layer containing NBPhen on thecathode 101 side and a layer containing a substance having anelectron-transport property on the anode 100 side. The following areexamples of the substance having an electron-transport propertycontained in the layer on the anode side of the electron-transportlayer: a metal complex such asbis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); aheterocyclic compound having a polyazole skeleton such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI) or2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); a heterocyclic compound having a diazineskeleton such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine(abbreviation: 4,6mPnP2Pm), or4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); a heterocyclic compound having a pyridine skeleton suchas 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy)or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB); and ananthracene derivative such as CzPA, PCzPA,3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), DPPA, DNA, t-BuDNA, or7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA). Among the above materials, a heterocycliccompound having a diazine skeleton and a heterocyclic compound having apyridine skeleton have high reliability and are thus preferable.Specifically, a heterocyclic compound having a diazine (pyrimidine orpyrazine) skeleton has a high electron-transport property to contributeto a reduction in drive voltage.

The layer containing a substance having an electron-transport propertyformed on the anode 100 side of the electron-transport layer (the layerin contact with the anode side of the layer containing NBPhen) ispreferably a layer containing a condensed aromatic compound or acondensed heteroaromatic compound because heat resistance of thelight-emitting element can be improved. The condensed aromatic compoundor the condensed heteroaromatic compound preferably has three or morecondensed rings. This structure functions more effectively when thelayer in contact with the anode side of the layer containing NBPhencontains the condensed heteroaromatic compound. That is, even when thecondensed heteroaromatic compound that is less stable than the condensedaromatic compound is used, by stacking the condensed heteroaromaticcompound and the layer containing NBPhen, heat resistance as in the caseof stacking the condensed aromatic compound and the layer containingNBPhen can be achieved. As the condensed heteroaromatic compound, acompound including two nitrogen atoms in one condensed ring ispreferable.

A light-emitting region corresponds to the layer containing alight-emitting substance which may be formed in contact with theelectron-transport layer or in the electron-transport layer. Thelight-emitting substance can be a fluorescent compound or aphosphorescent compound which is described below.

Examples of the fluorescent compound include:5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N-diphenylpyrene-1,6-diamine(abbreviation: 1,6FLPAPrn),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation:YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-bipheny-2-yl)-N-[4-(9H-carbaz-9-yl)phenyl-N-phenyanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i]]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM). Condensed aromatic diamine compounds typifiedby pyrenediamine compounds such as 1,6FLPAPrn and 1,6mMemFLPAPrn areparticularly preferable because of their high hole-trapping properties,high emission efficiency, and high reliability.

As the fluorescent compound, a substance exhibiting thermally activateddelayed fluorescence (TADF) can also be used. As a material exhibitingTADF, materials given below can be used.

A fullerene, a derivative thereof, an acridine derivative such asproflavine, and eosin can be given. Further, a metal-containingporphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn),cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd)can be given. Examples of the metal-containing porphyrin include aprotoporphyrin-tin fluoride complex (abbreviation: SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (abbreviation: SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (abbreviation: SnF₂(Hemato IX)), acoproporphyrin tetramethyl ester-tin fluoride complex (abbreviation:SnF₂(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex(abbreviation: SnF₂(OEP)), an etioporphyrin-tin fluoride complex(abbreviation: SnF₂(Etio I)), and an octaethylporphyrin-platinumchloride complex (abbreviation: PtCl₂(OEP)), which are represented bythe following structural formulae.

Alternatively, a heterocyclic compound including a t-electron richheteroaromatic ring and a π-electron deficient heteroaromatic ring canbe used, such as2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(abbreviation: PIC-TRZ), which is shown by the structural formula givenbelow. The heterocyclic compound is preferably used, because of theπ-electron rich heteroaromatic ring and the π-electron deficientheteroaromatic ring, for which the electron-transport property and thehole-transport property are high. Note that a substance in which theπ-electron rich heteroaromatic ring is directly bonded to the π-electrondeficient heteroaromatic ring is particularly preferably used becausethe donor property of the π-electron rich heteroaromatic ring and theacceptor property of the π-electron deficient heteroaromatic ring areboth increased and the energy difference between the S₁ level and the T₁level becomes small.

As examples of the phosphorescent substance, the following can be given:an organometallic iridium complex having a 4H-triazole skeleton, such astris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III)(abbreviation: Ir(mpptz-dmp)₃),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(1H)(abbreviation: Ir(Mptz)₃), ortris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPrptz-3b)₃); an organometallic iridium complex havinga 1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(Mptz1-mp)₃) ortris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Prptz1-Me)₃); an organometallic iridium complex havingan imidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: Ir(iPrpmi)₃) ortris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: Ir(dmpimpt-Me)₃); and an organometallic iridium complexin which a phenylpyridine derivative having an electron-withdrawinggroup is a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)), orbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)). These are compounds emittingblue phosphorescence and have an emission peak at 440 nm to 520 nm.

Further, the following can be used: an organometallic iridium complexhaving a pyrimidine skeleton, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:Ir(mppm)₃), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₃),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)),bis[2-(6-tert-butyl-4-pyrimidinyl-N3)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(endo- and exo-mixture) (abbreviation: Ir(nbppm)₂(acac)),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(mpmppm)₂(acac)), or(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: Ir(dppm)₂(acac)); an organometallic iridium complexhaving a pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)) or(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)); an organometallic iridium complexhaving a pyridine skeleton, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(ppy)₂(acac)), bis(benzo[h]quinolinato)iridium(II)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)₃),tris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),or bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(pq)₂(acac)); and a rare earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)). These are mainly compounds emitting greenphosphorescence and have an emission peak at 500 nm to 600 nm. Note thatan organometallic iridium complex having a pyrimidine skeleton hasdistinctively high reliability and emission efficiency and thus isespecially preferable.

Further, the following can be used: an organometallic iridium complexhaving a pyrimidine skeleton, such asbis[4,6-bis(3-methylphenyl)pyrimidinato](diisobutyrylmethano)iridium(III)(abbreviation: Ir(5mdppm)₂(dibm)),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridiumn(III)(abbreviation: Ir(5mdppm)₂(dpm)), orbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(d1npm)₂(dpm)); an organometallic iridium complexhaving a pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm)), or(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)); an organometallic iridium complexhaving a pyridine skeleton such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:Ir(piq)₃) orbis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)); a platinum complex such as2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and a rare earth metal complex such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)) ortris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). These are compounds emitting redphosphorescence and have an emission peak at 600 nm to 700 nm. Further,the organometallic iridium complexes having pyrazine skeletons canprovide red light emission with favorable chromaticity.

Various phosphorescent materials, other than the phosphorescentcompounds given above, may also be selected and used.

Note that the light-emitting region preferably has a structure in whichthese light-emitting substances are dispersed in a host material. Inaddition to the substances given as the substance having anelectron-transport property contained in the electron-transport layer, asubstance having a hole-transport property can also be used. As thesubstance having a hole-transport property, the substances given as thesubstance having a hole-transport property that can be used in thecharge generation layer can be used. The following are preferably used:a compound having an aromatic amine skeleton such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF), orN-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF); a compound having a carbazole skeleton such as1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), or3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound havinga thiophene skeleton such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III), or4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV); and a compound having a furan skeleton suchas 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation:DBF₃P-II) or4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II). Among the above materials, a compoundhaving an aromatic amine skeleton and a compound having a carbazoleskeleton are preferable because these compounds are highly reliable andhave high hole-transport properties to contribute to a reduction indrive voltage.

At least one light-emitting region may be included in each of thelight-emitting units. Alternatively, a plurality of light-emittinglayers containing different light-emitting substances and/or hostmaterials or a plurality of light-emitting layers containing the samelight-emitting substance and host material but in differentconcentrations may be included in each of the light-emitting units.Needless to say, structures of light-emitting layers in thelight-emitting units may be the same or different from each other.

Other than the electron-transport layer and the light-emitting layerincluded in each of the light-emitting units, a layer containing ahole-injection substance and having a hole-injection property (ahole-injection layer), a layer containing a hole-transport substance andhaving a hole-transport property (a hole-transport layer), a layercontaining a bipolar substance and having a bipolar property (havingboth an electron-transport property and a hole-transport property), andthe like can be given. Each of the light-emitting units can be formed byusing combination of the above layers and other various functionallayers as appropriate. Note that in the n-th light-emitting unit 102 nwhich is in contact with the cathode 101, a layer containing anelectron-injection substance and having an electron-injection property(an electron-injection layer) may be further provided as a layer whichis the closest to the cathode 101. Furthermore, a charge generationregion may be provided between the first light-emitting unit 102 k andthe anode 100 and between the n-th light-emitting unit 102 n and thecathode 101.

The hole-injection layer, the hole-transport layer, and theelectron-injection layer will be described below.

The hole-injection layer is a layer containing a substance having ahole-injection property. As the substance having a hole-injectionproperty, for example, a metal oxide such as molybdenum oxide, vanadiumoxide, ruthenium oxide, tungsten oxide, or manganese oxide can be used.Alternatively, it is possible to use a phthalocyanine-based compoundsuch as phthalocyanine (abbreviation: H₂Pc) or copper(II) phthalocyanine(abbreviation: CuPc). A polymer such as PEDOT/PSS (abbreviation) canalso be used.

The hole-transport layer is a layer containing a substance having ahole-transport property. As the substance having a hole-transportproperty contained in the hole-transport layer, a substance similar tothe substance having a hole-transport property contained in the abovecharge generation region 104 can be used. Thus, the above description isreferred to here. Note that the hole-transport layer may have a stackedstructure of two or more layers containing the above substances as wellas a single-layer structure.

The electron-injection layer which can be provided in the n-thlight-emitting unit 102 n contains a substance having anelectron-injection property. As the substance having anelectron-injection property, the following can be given: an alkalimetal, an alkaline earth metal, and a compound of these metals, such aslithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride(CaF₂). Alternatively, a substance having an electron-transport propertycontaining an alkali metal, an alkaline earth metal, or a compound ofthese metals (e.g., Alq (abbreviation) containing magnesium (Mg)) can beused as the substance having an electron-injection property. Such astructure makes it possible to increase the efficiency of electroninjection from the cathode 101.

A charge generation region may be provided between the firstlight-emitting unit 102 k and the anode 100 or between the n-thlight-emitting unit 102 n and the cathode 101. In the case where acharge generation region is provided between the first light-emittingunit 102 k and the anode 100 or between the n-th light-emitting unit 102n and the cathode 101, the charge generation region is formed using acomposite material containing a substance having a hole-transportproperty and an acceptor substance. The charge generation region is notlimited to containing the substance having a hole-transport property andthe acceptor substance in the same film, and may be a stack of a layercontaining the substance having a hole-transport property and a layercontaining the acceptor substance. Note that, in the case of the stackedstructure, the layer containing an acceptor substance is in contact withthe anode 100 or the cathode 101.

When a charge generation region is provided between the firstlight-emitting unit 102 k and the anode 100 or between the n-thlight-emitting unit 102 n and the cathode 101, the anode 100 or thecathode 101 can be formed without consideration of a work function of asubstance for forming the electrodes. Note that a structure and asubstance similar to those of the above charge generation region 104 canbe used for the charge generation region which is provided between thefirst light-emitting unit 102 k and the anode 100 or between the n-thlight-emitting unit 102 n and the cathode 101. Therefore, the abovedescription is referred to.

Note that each of the light-emitting units can be formed by stacking theabove layers in appropriate combination. As a formation method of eachof the light-emitting units, a variety of methods (e.g., a dry processsuch as a vacuum evaporation method, a wet process such as an ink-jetmethod or a spin coating method, or the like) can be used depending on amaterial to be used. Each layer may be formed by a different formationmethod.

The anode 100 is preferably formed using a metal, an alloy, a conductivecompound, a mixture thereof, or the like which has a high work function(specifically, a work function of higher than or equal to 4.0 eV).Specific examples include indium oxide-tin oxide (ITO: indium tinoxide), indium oxide-tin oxide containing silicon or silicon oxide,indium oxide-zinc oxide, and indium oxide containing tungsten oxide andzinc oxide (IWZO). Such conductive metal oxide films are usually formedby a sputtering method, but may be formed by application of a sol-gelmethod or the like. In an example of the formation method, indiumoxide-zinc oxide is deposited by a sputtering method using a targetobtained by adding 1 wt % to 20 wt % of zinc oxide to indium oxide.Further, indium oxide containing tungsten oxide and zinc oxide (IWZO)can be deposited by a sputtering method by using a target in whichtungsten oxide and zinc oxide are added to indium oxide at 0.5 wt % to 5wt % and 0.1 wt % to 1 wt %, respectively. Alternatively, gold (Au),platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum(Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), a nitride ofa metal material (e.g., titanium nitride), or the like can be used.Graphene can also be used.

The cathode 101 can be formed by using a metal, an alloy, anelectrically conductive compound, a mixture thereof, or the like thathas a low work function (specifically, a work function of lower than orequal to 3.8 eV). Specific examples of such a cathode material areelements belonging to Groups 1 and 2 of the periodic table, such asalkali metals (e.g., lithium (Li) and cesium (Cs)), magnesium (Mg),calcium (Ca), and strontium (Sr), alloys thereof (e.g., MgAg and AlLi),rare earth metals such as europium (Eu) and ytterbium (Yb), alloysthereof, and the like. However, when the electron-injection layer isprovided between the cathode 101 and the electron-transport layer, anyof a variety of conductive materials such as Al, Ag, ITO, indiumoxide-tin oxide containing silicon or silicon oxide, and the like can beused regardless of its work function as the cathode 101. Theseconductive materials can be deposited by a sputtering method, an ink-jetmethod, a spin coating method, or the like.

Note that in the light-emitting element described in this embodiment, atleast one of the anode 100 and the cathode 101 may have a property oftransmitting visible light. The light-transmitting property can beensured by using a transparent electrode such as ITO or by reducing thethickness of an electrode. Alternatively, a stacked structure of a thinmaterial and a transparent electrode may be used.

In addition, a conductive layer for controlling the optical path lengthof the light-emitting element may be formed between the anode 100 andthe light-emitting unit or between the cathode 101 and thelight-emitting unit by using a light-transmitting conductive materialsuch as ITO.

Since the light-emitting element of this embodiment includes a pluralityof light-emitting units, light that is a combination of light emittedfrom respective light-emitting units can be obtained. In other words, inthe case where a plurality of light-emitting units each including alight-emitting layer containing the same light-emitting substance isstacked, higher luminance can be obtained as compared to alight-emitting element formed by using only one light-emitting unit whenthe current density is the same. Further, in the case where thelight-emitting element of this embodiment is formed by stacking thelight-emitting units containing light-emitting substances exhibitingdifferent emission colors, a light-emitting element having a broadspectrum or a light-emitting element exhibiting white light emission canbe obtained. A display including a light-emitting element exhibitingwhite light emission and a color filter is advantageous in achievinghigher definition.

Therefore, even when the light-emitting element having the abovestructure in this embodiment in which a plurality of light-emittingunits is separated from each other by a charge generation layer is usedin a high-definition display (e.g., a distance between light-emittingregions of adjacent light-emitting elements is shorter than or equal to40 μm), an interference phenomenon between the adjacent light-emittingelements can be effectively reduced without great increase in drivingvoltage and the display can provide a high-quality image. Note that thelight-emitting element in which a plurality of light-emitting units isseparated from each other by a charge generation region is alight-emitting element which easily realizes a high current efficiency,a broad emission spectrum, or white light emission.

Embodiment 2

This embodiment shows a light-emitting device including thelight-emitting element described in Embodiment 1.

In this embodiment, the light-emitting device manufactured by using thelight-emitting element described in Embodiment 1 will be described withreference to FIGS. 2A and 2B. FIG. 2A is a top view illustrating thelight-emitting device, and FIG. 2B is a cross-sectional view of FIG. 2Ataken along lines A-B and C-D. This light-emitting device includes adriver circuit portion (source line driver circuit) 601, a pixel portion602, and a driver circuit portion (gate line driver circuit) 603, whichare to control light emission of a light-emitting element andillustrated with dotted lines. A reference numeral 604 denotes a sealingsubstrate; 605 denotes a sealant; and a portion surrounded by thesealant 605 is a space 607.

A lead wiring 608 is a wiring for transmitting signals to be input tothe source line driver circuit 601 and the gate line driver circuit 603and receiving a video signal, a clock signal, a start signal, a resetsignal, and the like from an FPC (flexible printed circuit) 609 servingas an external input terminal. Although only the FPC is shown here, theFPC may be provided with a printed wiring board (PWB). Thelight-emitting device in this specification includes not only a mainbody of the light-emitting device but also the light-emitting devicewith an FPC or a PWB attached.

Next, a cross-sectional structure will be described with reference toFIG. 2B. The driver circuit portion and the pixel portion are formedover an element substrate 610; FIG. 2B shows the source line drivercircuit 601, which is a driver circuit portion, and one of the pixels inthe pixel portion 602.

As the source line driver circuit 601, a CMOS circuit in which ann-channel TFT 623 and a p-channel TFT 624 are combined is formed. Thedriver circuit may be formed with various types of CMOS circuits, PMOScircuits, or NMOS circuits. A driver integration type in which a drivercircuit is formed over a substrate is described in this embodiment, butit is not necessarily required and a driver circuit can be formedoutside a substrate, not over the substrate.

The pixel portion 602 includes a plurality of pixels, each of whichincludes a switching TFT 611, a current control TFT 612, and a firstelectrode 613 which is electrically connected to a drain of the currentcontrol TFT 612. Note that an insulator 614 is formed to cover an edgeof the first electrode 613. Here, a positive type photosensitive acrylicresin film is used to form the insulator 614.

The insulator 614 is formed to have a curved surface with curvature atan upper edge or a lower edge thereof in order to obtain favorablecoverage. For example, in the case of using positive type photosensitiveacrylic as a material of the insulator 614, the insulator 614 ispreferably formed to have a curved surface with a curvature radius (0.2μm to 3 μm) only at an upper edge. As the insulator 614, either anegative type photosensitive resin or a positive type photosensitiveresin can be used.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. In this case, it is preferable that the first electrode613 serving as an anode be formed by using a material with a high workfunction. For example, a single-layer film of an ITO film, an indium tinoxide film containing silicon, an indium oxide film containing 2 wt % to20 wt % of zinc oxide, a titanium nitride film, a chromium film, atungsten film, a Zn film, a Pt film, or the like can be used. Besidesthese single-layer films, a stack of a titanium nitride film and a filmcontaining aluminum as its main component, a stack of three layers of atitanium nitride film, a film containing aluminum as its main component,and a titanium nitride film, or the like can be used. When the firstelectrode 613 has a stacked structure, resistance as a wiring is low, agood ohmic contact is formed, and further, the first electrode 613 canbe made to function as an anode.

In addition, the EL layer 616 is formed by various methods such as anevaporation method using an evaporation mask, an ink-jet method, or aspin coating method. The EL layer 616 has the structure described inEmbodiment 1. As another material included in the EL layer 616, a lowmolecular compound or a high molecular compound (including an oligomeror a dendrimer) may be used.

As a material used for the second electrode 617, which is formed overthe EL layer 616 and functions as a cathode, a material having a lowwork function (e.g., Al, Mg, Li, Ca, or an alloy or a compound thereof,such as MgAg, MgIn, or AlLi) is preferably used. When light generated inthe EL layer 616 passes through the second electrode 617, the secondelectrode 617 is preferably formed from a stack of a thin metal film anda transparent conductive film (ITO, indium oxide containing 2 wt % to 20wt % of zinc oxide, indium tin oxide containing silicon, zinc oxide(ZnO), or the like).

Note that the light-emitting element is formed with the first electrode613, the EL layer 616, and the second electrode 617. The light-emittingelement has the structure described in Embodiment 1. In thelight-emitting device in this embodiment, the pixel portion, whichincludes a plurality of light-emitting elements, may include both thelight-emitting element described in Embodiment 1 and a light-emittingelement having a different structure.

By attaching the sealing substrate 604 to the element substrate 610 withthe sealant 605, a light-emitting element 618 is provided in the space607 surrounded by the element substrate 610, the sealing substrate 604,and the sealant 605. The space 607 is filled with filler, but there isalso a case where the space 607 is filled with an inert gas (nitrogen,argon, or the like) or filled with the sealant 605. It is preferablethat the sealing substrate be provided with a recessed portion and adrying agent be provided in the recessed portion, in which casedeterioration due to influence of moisture can be suppressed.

An epoxy-based resin or glass frit is preferably used for the sealant605. Such a material preferably allows as little moisture and oxygen aspossible to penetrate. As the sealing substrate 604, a glass substrate,a quartz substrate, or a plastic substrate formed of fiber reinforcedplastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic, or thelike can be used.

In this manner, it is possible to obtain the light-emitting device usingthe light-emitting element described in Embodiment 1.

Since the light-emitting device in this embodiment is formed by usingthe light-emitting element described in Embodiment 1, a light-emittingdevice having favorable characteristics can be provided. Specifically,since the light-emitting element described in Embodiment 1 has favorableemission efficiency, the light-emitting device can have reduced powerconsumption. In addition, since the light-emitting element is easy tomass-produce, the light-emitting device can be provided at low cost.

FIGS. 3A and 3B each illustrate an example of a light-emitting device inwhich full color display is achieved by formation of a light-emittingelement exhibiting white light emission and using coloring layers (colorfilters) and the like. In FIG. 3A, a substrate 1001, a base insulatingfilm 1002, a gate insulating film 1003, gate electrodes 1006, 1007, and1008, a first interlayer insulating film 1020, a second interlayerinsulating film 1021, a peripheral portion 1042, a pixel portion 1040, adriver circuit portion 1041, first electrodes 1024W, 1024R, 1024G, and1024B of light-emitting elements, a partition wall 1025, an EL layer1028, a second electrode 1029 of the light-emitting elements, a sealingsubstrate 1031, a sealant 1032, and the like are illustrated.

In FIG. 3A, coloring layers (a red coloring layer 1034R, a greencoloring layer 1034G, and a blue coloring layer 1034B) are provided on atransparent base material 1033. Further, a black layer (black matrix)1035 may be provided. The transparent base material 1033 provided withthe coloring layers and the black layer is positioned and fixed to thesubstrate 1001. Note that the coloring layers and the black layer arecovered with an overcoat layer 1036. In FIG. 3A, light emitted from someof the light-emitting layers does not pass through the coloring layers,while light emitted from the others of the light-emitting layers passesthrough the coloring layers. Since light which does not pass through thecoloring layers is white and light which passes through any one of thecoloring layers is red, blue, or green, an image can be displayed usingpixels of the four colors.

FIG. 3B illustrates an example in which the coloring layers (the redcoloring layer 1034R, the green coloring layer 1034G, and the bluecoloring layer 1034B) are provided between the gate insulating film 1003and the first interlayer insulating film 1020. As in this structure, thecoloring layers may be provided between the substrate 1001 and thesealing substrate 1031.

The above-described light-emitting device is a light-emitting devicehaving a structure in which light is extracted from the substrate 1001side where the TFTs are formed (a bottom emission structure), but may bea light-emitting device having a structure in which light is extractedfrom the sealing substrate 1031 side (a top emission structure). FIG. 4is a cross-sectional view of a light-emitting device having a topemission structure. In this case, as the substrate 1001, a substratethat does not transmit light can be used. The process up to the step offorming a connection electrode which connects the TFT and the anode ofthe light-emitting element is performed in a manner similar to that ofthe light-emitting device having a bottom emission structure. Then, athird interlayer insulating film 1037 is formed to cover an electrode1022. This insulating film may function for planarization. The thirdinterlayer insulating film 1037 can be formed by using a materialsimilar to that of the second interlayer insulating film, or can beformed by using any other known materials.

The first electrodes 1024W, 1024R, 1024G, and 1024B of thelight-emitting elements each serve as an anode here, but may serve as acathode. Further, in the case of a light-emitting device having a topemission structure as illustrated in FIG. 4, the first electrodes arepreferably reflective electrodes. The EL layer 1028 is formed to have astructure similar to the structure of the EL layer 110, which isdescribed in Embodiment 1 and with which white light emission can beobtained.

In the case of a top emission structure as illustrated in FIG. 4,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G, and the blue coloring layer 1034B) are provided. The black layer(black matrix) 1035 may be provided on the sealing substrate 1031 so asto be located between the pixels. The coloring layers (the red coloringlayer 1034R, the green coloring layer 1034G, and the blue coloring layer1034B) and the black layer (the black matrix) may be covered with theovercoat layer. Note that a light-transmitting substrate is used as thesealing substrate 1031.

Further, although an example in which full color display is performedusing four colors of red, green, blue, and white is shown here, there isno particular limitation and full color display may be performed usingthree colors of red, green, and blue.

Since the light-emitting device in this embodiment is formed using thelight-emitting element described in Embodiment 1, a light-emittingdevice having favorable characteristics can be provided. Specifically,since the light-emitting element described in Embodiment 1 has favorableemission efficiency, the light-emitting device can have reduced powerconsumption. In addition, since the light-emitting element is easy tomass-produce, the light-emitting device can be provided at low cost.

Since many minute light-emitting elements arranged in a matrix in thelight-emitting device described above can each be controlled, thelight-emitting device can be suitably used as a display device fordisplaying images.

This embodiment can be freely combined with any of the otherembodiments.

Embodiment 3

In this embodiment, examples of an electronic device including thelight-emitting element described in Embodiment 1 as part thereof will bedescribed. The light-emitting element described in Embodiment 1 has highemission efficiency and consumes low power, and by using thelight-emitting element, a display can provide high display quality. As aresult, the electronic devices described in this embodiment can eachhave a display portion having high display quality and reduced powerconsumption.

Examples of the electronic device to which the above light-emittingelement is applied include television devices (also referred to as TV ortelevision receivers), monitors for computers and the like, cameras suchas digital cameras and digital video cameras, digital photo frames,mobile phones (also referred to as cell phones or mobile phone devices),portable game machines, portable information terminals, audio playbackdevices, large game machines such as pachinko machines, and the like.Specific examples of these electronic devices are given below.

FIG. 5A illustrates an example of a television device. In the televisiondevice, a display portion 7103 is incorporated in a housing 7101. Inaddition, here, the housing 7101 is supported by a stand 7105. Imagescan be displayed on the display portion 7103, and in the display portion7103, the light-emitting elements described in Embodiment 1 are arrangedin a matrix.

The television device can be operated with an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device is provided with a receiver, a modem,and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 5B1 illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer is manufactured by using light-emitting elements arrangedin a matrix in the display portion 7203, which are the same as thatdescribed in Embodiment 1. The computer illustrated in FIG. 5B1 may havea structure illustrated in FIG. 5B2. The computer illustrated in FIG.5B2 is provided with a second display portion 7210 instead of thekeyboard 7204 and the pointing device 7206. The second display portion7210 is a touch screen, and input can be performed by operation ofdisplay for input on the second display portion 7210 with a finger or adedicated pen. The second display portion 7210 can also display imagesother than the display for input. The display portion 7203 may also be atouch screen. Connecting the two screens with a hinge can preventtroubles; for example, the screens can be prevented from being crackedor broken while the computer is being stored or carried.

FIG. 5C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 including the light-emitting elements arranged ina matrix which are described in Embodiment 1 is incorporated in thehousing 7301, and a display portion 7305 is incorporated in the housing7302. In addition, the portable game machine illustrated in FIG. 5Cincludes a speaker portion 7306, a recording medium insertion portion7307, an LED lamp 7308, input means (an operation key 7309, a connectionterminal 7310, a sensor 7311 (a sensor having a function of measuringforce, displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and a microphone 7312), and thelike. Needless to say, the structure of the portable game machine is notlimited to the above as long as the display portion including thelight-emitting elements described in Embodiment 1 and arranged in amatrix is used as at least either the display portion 7304 or thedisplay portion 7305, or both, and the structure can include otheraccessories as appropriate. The portable game machine illustrated inFIG. 5C has a function of reading out a program or data stored in astorage medium to display it on the display portion, and a function ofsharing information with another portable game machine by wirelesscommunication. The portable game machine illustrated in FIG. 5C can havea variety of functions without limitation to the above.

FIG. 5D illustrates an example of a mobile phone. The mobile phone isprovided with a display portion 7402 incorporated in a housing 7401, anoperation button 7403, an external connection port 7404, a speaker 7405,a microphone 7406, and the like. Note that the mobile phone 7400 has thedisplay portion 7402 including the light-emitting elements described inEmbodiment 1 and arranged in a matrix.

When the display portion 7402 of the mobile phone illustrated in FIG. 5Dis touched with a finger or the like, data can be input into the mobilephone. In this case, operations such as making a call and creating ane-mail can be performed by touching the display portion 7402 with afinger or the like.

There are mainly three screen modes for the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting data such as characters. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are combined.

For example, in the case of making a call or creating e-mail, acharacter input mode mainly for inputting characters is selected for thedisplay portion 7402 so that characters displayed on the screen can beinput. In this case, it is preferable to display a keyboard or numberbuttons on almost the entire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone, display on the screen of the display portion 7402 can beautomatically changed by determining the orientation of the mobile phone(whether the mobile phone is placed horizontally or vertically for alandscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 can function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

As described above, the application range of the light-emitting deviceincluding the light-emitting elements described-in Embodiment 1 isextremely wide; therefore, the light-emitting device can be applied toelectronic devices of a variety of fields. By using the light-emittingelements described in Embodiment 1, electronic devices which can providehigh-quality display and consumes low power can be obtained.

The light-emitting element described in Embodiment 1 can also be usedfor an automobile windshield or an automobile dashboard. FIG. 6illustrates one mode in which the light-emitting elements described inEmbodiment 1 are used for an automobile windshield and an automobiledashboard. Display regions 5000 to 5005 each include the light-emittingelement described in Embodiment 1.

The display region 5000 and the display region 5001 are display deviceswhich are provided in the automobile windshield and in which thelight-emitting elements described in Embodiment 1 are incorporated. Thelight-emitting element described in Embodiment 1 can be formed into whatis called a see-through display device, through which the opposite sidecan be seen, by including a first electrode and a second electrodeformed of electrodes having light-transmitting properties. Suchsee-through display devices can be provided even in the automobilewindshield without hindering the view. Further, in the case where atransistor for driving is provided, it is preferable to use a transistorhaving a light-transmitting property, such as an organic transistorusing an organic semiconductor material or a transistor using an oxidesemiconductor.

A display device incorporating the light-emitting element described inEmbodiment 1 is provided in the display region 5002 in a pillar portion.The display region 5002 can compensate for the view hindered by thepillar portion by showing an image taken by an imaging unit provided inthe car body. Similarly, the display region 5003 provided in thedashboard can compensate for the view hindered by the car body byshowing an image taken by an imaging unit provided in the outside of thecar body, which leads to elimination of blind areas and enhancement ofsafety. Showing an image so as to compensate for the area which a drivercannot see, makes it possible for the driver to confirm safety easilyand comfortably.

The display region 5004 and the display region 5005 can provide avariety of kinds of information such as navigation data, a speedometer,a tachometer, a mileage, a fuel meter, a gearshift indicator, andair-condition setting. The contents or layout of the display can bechanged by a user as appropriate. Note that such information can also beshown by the display regions 5000 to 5003. The display regions 5000 to5005 can also be used as lighting devices.

The light-emitting element described in Embodiment 1 can have highemission efficiency and low power consumption. Therefore, load on abattery is small even when a number of large screens such as the displayregions 5000 to 5005 are provided, which provides comfortable use. Forthat reason, the light-emitting device or the lighting device whichincludes the light-emitting element described in Embodiment 1 can besuitably used as an in-vehicle light-emitting device or an in-vehiclelighting device. Since the light-emitting element according to oneembodiment of the present invention has high heat resistance, thelight-emitting device which includes the light-emitting elementdescribed in Embodiment 1 is highly preferable as an in-vehicle displaydevice which must resist high temperature particularly in summer.

FIGS. 7A and 7B illustrate an example of a foldable tablet terminal. InFIG. 7A, the tablet terminal is opened, and includes a housing 9630, adisplay portion 9631 a, a display portion 9631 b, a switch 9034 forswitching display modes, a power button 9035, a switch 9036 forswitching to power-saving mode, and a clip 9033. Note that in the tabletterminal, one or both of the display portion 9631 a and the displayportion 9631 b is/are formed using the light-emitting device whichincludes the light-emitting element described in Embodiment 1.

Part of the display portion 9631 a can be a touch screen region 9632 aand data can be input when a displayed operation key 9637 is touched.Note that, as an example, half of the area of the display portion 9631 ahas only a display function and the other half of the area has a touchscreen function. However, the structure of the display portion 9631 a isnot limited to this, and all the area of the display portion 9631 a mayhave a touch screen function. For example, all the area of the displayportion 9631 a can display keyboard buttons and serve as a touch screenwhile the display portion 9631 b can be used as a display screen.

Like the display portion 9631 a, part of the display portion 9631 b canbe a touch screen region 9632 b. When a keyboard display switchingbutton 9639 displayed on the touch screen is touched with a finger, astylus, or the like, a keyboard can be displayed on the display portion9631 b.

Touch input can be performed in the touch screen region 9632 a and thetouch screen region 9632 b at the same time.

The switch 9034 for switching display modes can switch the displaybetween portrait mode, landscape mode, and the like, and betweenmonochrome display and color display, for example. The switch 9036 forswitching to power-saving mode can control display luminance to beoptimal in accordance with the amount of external light in use of thetablet terminal detected by an optical sensor incorporated in the tabletterminal. In addition to the optical sensor, other detecting devicessuch as sensors for determining inclination, such as a gyroscope or anacceleration sensor, may be incorporated in the tablet terminal.

Although the display portion 9631 a and the display portion 9631 b havethe same display area in FIG. 7A, one embodiment of the presentinvention is not limited to this example. The display portion 9631 a andthe display portion 9631 b may have different areas or different displayquality. For example, one of the display portions 9631 a and 9631 b maydisplay higher definition images than the other.

FIG. 7B illustrates the tablet terminal which is folded. The tabletterminal in this embodiment includes the housing 9630, a solar cell9633, a charge and discharge control circuit 9634, a battery 9635, and aDCDC converter 9636. Note that FIG. 7B shows an example in which thecharge and discharge control circuit 9634 includes the battery 9635 andthe DCDC converter 9636.

Since the tablet terminal is foldable, the housing 9630 can be closedwhen the tablet terminal is not used. As a result, the display portion9631 a and the display portion 9631 b can be protected; thus, a tabletterminal which has excellent durability and excellent reliability interms of long-term use can be provided.

The tablet terminal illustrated in FIGS. 7A and 7B can have otherfunctions such as a function of displaying various kinds of data (e.g.,a still image, a moving image, and a text image), a function ofdisplaying a calendar, a date, the time, or the like on the displayportion, a touch-input function of operating or editing the datadisplayed on the display portion by touch input, and a function ofcontrolling processing by using various kinds of software (programs).

The solar cell 9633, which is attached on the surface of the tabletterminal, supplies power to a touch screen, a display portion, an imagesignal processor, and the like. Note that the solar cell 9633 ispreferably provided on one or two surfaces of the housing 9630, in whichcase the battery 9635 can be charged efficiently.

The structure and the operation of the charge and discharge controlcircuit 9634 illustrated in FIG. 7B will be described with reference toa block diagram in FIG. 7C. FIG. 7C illustrates the solar cell 9633, thebattery 9635, the DCDC converter 9636, a converter 9638, switches SW1 toSW3, and the display portion 9631. The battery 9635, the DCDC converter9636, the converter 9638, and the switches SW1 to SW3 correspond to thecharge and discharge control circuit 9634 in FIG. 7B.

First, an example of operation in the case where power is generated bythe solar cell 9633 using external light is described. The voltage ofpower generated by the solar cell is raised or lowered by the DCDCconverter 9636 so that the power has a voltage for charging the battery9635. Then, when power supplied by the solar cell 9633 is used for theoperation of the display portion 9631, the switch SW1 is turned on andthe voltage of the power is raised or lowered by the converter 9638 soas to be voltage needed for the display portion 9631. In addition, whendisplay on the display portion 9631 is not performed, the switch SW1 isturned off and the switch SW2 is turned on so that charge of the battery9635 may be performed.

Although the solar cell 9633 is described as an example of a powergeneration means, the power generation means is not particularlylimited, and the battery 9635 may be charged by another power generationmeans such as a piezoelectric element or a thermoelectric conversionelement (Peltier element). The battery 9635 may be charged by anon-contact power transmission module which is capable of charging bytransmitting and receiving power by wireless (without contact), oranother charge means used in combination, and the power generation meansis not necessarily provided.

One embodiment of the present invention is not limited to the tabletterminal having the shape illustrated in FIGS. 7A to 7C as long as thedisplay portion 9631 is included.

Example 1

In this example, a light-emitting element according to one embodiment ofthe present invention (example elements 1-R, 1-G, and 1-B) and acomparative example (comparative example elements 1-R, 1-G, and 1-B)will be described. An element structure is shown in FIG. 13. In thisexample and the comparative example, display devices were fabricated byusing the above-described elements and then evaluated. In order tofabricate the display devices, for both the example element 1 and thecomparative example element 1, a color filter and a resonant structurewere used and three kinds of pixels, a red pixel, a green pixel, and ablue pixel, were used. Chemical formulae of organic compounds used inthe example elements 1-R, 1-G, and 1-B and the comparative exampleelements 1-R, 1-G, and 1-B are shown below.

Now, a method for fabricating the light-emitting element of this example(the example elements 1-R, 1-G, and 1-B) will be described.

(Method for Fabricating the Example Elements 1-R, 1-G, and 1-B)

Over a substrate formed of glass, an aluminum-nickel-lanthanum alloyfilm and a titanium film were sequentially formed by a sputteringmethod, whereby an anode 100 was formed. The thickness of thealuminum-nickel-lanthanum alloy film was 200 nm and the thickness of thetitanium film was 6 nm. In addition, the electrode area was 2 mm×2 mm.

Then, indium tin oxide containing silicon oxide (ITSO) was depositedover the anode 100 by a sputtering method, whereby a first conductivelayer 107 was formed. In order to have a microcavity effect, thethickness of the first conductive layer 107 was set to 75 nm, 40 nm, and10 nm in the example element 1-R, the example element 1-G, and theexample element 1-B, respectively.

Next, in pretreatment for forming the light-emitting element over thesubstrate, a surface of the substrate was washed with water and baked at200° C. for 1 hour, and then UV ozone treatment was performed for 370seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus whose pressure was reduced to about 10⁻⁴ Pa, vacuum baking wasperformed at 170° C. in a heating chamber of the vacuum evaporationapparatus for 30 minutes, and then the substrate was cooled down forabout 30 minutes.

Then, the substrate over which the anode 100 was formed was fixed to asubstrate holder provided in the vacuum evaporation apparatus so thatthe surface over which the anode 100 was formed faced downward. Thepressure in the vacuum evaporation apparatus was reduced to about 10⁻⁴Pa. After that, on the anode 100,3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn)represented by the above structural formula (I) and molybdenum(VI) oxidewere deposited by co-evaporation by an evaporation method usingresistance heating, whereby a first hole-injection layer 111_1 wasformed. The thickness of the first hole-injection layer 111_1 was 8.5nm, 13.5 nm, and 5 nm in the example element 1-R, the example element1-G, and the example element 1-B, respectively. The weight ratio ofPCPPn to molybdenum oxide was adjusted to 1:0.5 (=PCPPn:molybdenumoxide). Note that a co-evaporation method refers to an evaporationmethod in which evaporation is carried out from a plurality ofevaporation sources at the same time in one treatment chamber.

Next, on the first hole-injection layer 111_1, PCPPn was deposited to athickness of 10 nm, whereby a first hole-transport layer 112_1 wasformed.

Further, on the first hole-transport layer 112_1,9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (II) andN,N-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation:1,6mMemFLPAPrn) represented by the above structuralformula (iii) were deposited by co-evaporation to a thickness of 25 nmso that the weight ratio of CzPA to 1,6mMemFLPAPrn was 1:0.05(=CzPA:1,6mMemFLPAPrn), whereby a first light-emitting layer 113_1 wasformed.

After that, CzPA was deposited to a thickness of 5 nm, and2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBPhen) represented by the above structural formula (Iv) was depositedto a thickness of 15 nm, whereby a first electron-transport layer 114_1was formed. Components from the first hole-injection layer 111_1 to thefirst electron-transport layer 114_1 are collectively referred to as afirst light-emitting unit 102_1.

A charge generation layer 103 was formed on the first light-emittingunit 102_1. The charge generation layer 103 was formed in the followingmanner. First, as part of an electron-injection buffer region 105, alithium layer was formed by using lithium oxide. The thickness thereofwas 0.1 nm. Then, as an electron-relay region, copper phthalocyanine(abbreviation: CuPC) represented by the above structural formula (v) wasdeposited to a thickness of 2 nm. After that, as a charge generationregion 104, 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene)(abbreviation: DBT3P-II) represented by the above structural formula(vi) and molybdenum(VI) oxide were deposited by co-evaporation to athickness of 12.5 nm. Note that the weight ratio of DBT3P-II tomolybdenum oxide was adjusted to 1:0.5 (=DBT3P-II: molybdenum oxide).

Next, on the charge generation layer 103,4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)represented by the above structural formula (vii) was deposited to athickness of 20 nm as a second hole-transport layer 112_2.

Then, 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) represented by the above structuralformula (viii),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB) represented by the above structural formula (ix),andbis[2-(6-tert-butyl-4-pyrimidinyl-N3)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)) represented by the above structuralformula (x) were deposited by co-evaporation to a thickness of 20 nm sothat the weight ratio of 2mDBTBPDBq-II to PCBNBB and Ir(tBuppm)₂(acac)was 0.7:0.3:0.06 (=2mDBTBPDBq-II:PCBNBB:Ir(tBuppm)₂(acac)). After that,2mDBTBPDBq-II andbis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(dmdppr-P)₂(dibm)) represented by the above structuralformula (xi) were deposited by co-evaporation to a thickness of 20 nm sothat the weight ratio of 2mDBTBPDBq-II to Ir(dmdppr-P)₂(dibm) was 1:0.04(=2mDBTBPDBq-II:Ir(dmdppr-P)₂(dibm)), whereby a second light-emittinglayer 113_2 was formed.

After that, on the second light-emitting layer 113_2, 2mDBTBPDBq-II wasdeposited to a thickness of 30 nm, and NBPhen was deposited to athickness of 15 nm, whereby a second electron-transport layer 114_2 wasformed.

After the second electron-transport layer 114_2 was formed, lithiumfluoride (LiF) was deposited by evaporation to a thickness of 1 nm,whereby an electron-injection layer 115_2 was formed. Finally, as acathode 101, a silver-magnesium alloy was deposited to a thickness of 15nm and indium tin oxide (ITO) was deposited to a thickness of 70 nm.Accordingly, the light-emitting element of this example (the exampleelements 1-R, 1-G, and 1-B) was fabricated. Components from the secondhole-transport layer 112_2 to the electron-injection layer 115_2correspond to a second light-emitting unit 102_2.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

Now, a method for fabricating the comparative light-emitting element ofthis example (the comparative example elements 1-R, 1-G, and 1-B) willbe described.

(Method for Fabricating the Comparative Example Elements 1-R, 1-G, and1-B)

The comparative example element 1-R was obtained by setting thethickness of the first hole-injection layer 111_1 in the exampleelements 1-R, 1-G, and 1-B to 13.5 nm. The comparative example element1-G was obtained by setting the thickness of the first hole-injectionlayer 111_1 in the example elements 1-R, 1-G, and 1-B to 16 nm. Thecomparative example element 1-B was obtained by setting the thickness ofthe first hole-injection layer 111_1 in the example elements 1-R, 1-G,and 1-B to 7.5 nm. Furthermore, the first electron-transport layer 114_1and the second electron-transport layer 114_2 were formed by usingbathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (xii) instead of NBPhen. Other components were formedin a manner similar to those of the example elements 1-R, 1-G, and 1-B.

The example elements 1-R, 1-G, and 1-B and the comparative exampleelements 1-R, 1-G, and 1-B were each sealed by using a glass substrateprovided with a color filter in a glove box containing a nitrogenatmosphere so as not to be exposed to the air (specifically, a sealantwas applied onto an outer edge of the element and UV treatment and heattreatment at 80° C. for 1 hour were performed at the time of sealing).Then, characteristics of these light-emitting elements were measured.Note that the measurements were performed at room temperature (in anatmosphere kept at 25° C.).

Next, a method for measuring the characteristics of the example elements1-R, 1-G, and 1-B and the comparative example elements 1-R, 1-G, and 1-Bwill be described.

The fabricated red elements (the example element 1-R and the comparativeexample element 1-R) were provided with a color filter layer CF(R), thefabricated green elements (the example element 1-G and the comparativeexample element 1-G) were provided with a color filter layer CF(G), andthe fabricated blue elements (the example element 1-B and thecomparative example element 1-B) were provided with a color filter layerCF(B). In this state, the element characteristics were measured.

The color filter layer CF(R), the color filter layer CF(G), and thecolor filter layer CF(B) were formed in such a manner that CR-7001W,CG-7001W, and CB-7001W (each manufactured by FUJIFILM Corporation) whichwere each used as a material were applied onto a glass substrate, andthen baked at 220° C. for 1 hour. The thickness of the color filterlayer was 1.3 μm to 1.4 μm. Note that the color filter materials wereapplied onto the glass substrate by a spin coating method at a spinningrate of 500 rpm for the color filter layer CF(R), at a spinning rate of1000 rpm for the color filter layer CF(G), and at a spinning rate of2000 rpm for the color filter layer CF(B).

FIG. 8 shows the current density-luminance characteristics of theexample elements 1-R, 1-G, and 1-B and the comparative example elements1-R, 1-G, and 1-B, FIG. 9 show the luminance-current efficiencycharacteristics thereof, FIG. 10 shows the voltage-luminancecharacteristics thereof, and FIG. 11 shows the emission spectra.

As seen from the above, it was found that there are no large differencesbetween the initial characteristics of the example elements 1-R, 1-G,and 1-B and the comparative example elements 1-R, 1-G, and 1-B.

Next, the reliability of the example elements 1-R, 1-G, and 1-B wasexamined. FIG. 14 is a graph showing the change in luminance withrespect to the driving time under the condition that the initialluminance of the example element 1-R was 655 cd/m², the initialluminance of the example element 1-G was 1667 cd/m², the initialluminance of the example element 1-B was 249 cd/m², and each initialluminance was set to 100% with the current efficiency constant. Theinitial luminance of each element was a value of the luminance ratio ofa white light-emitting element that has chromaticity of D65 and isfabricated by using these elements.

From FIG. 14, it was found that the example elements 1-R, 1-G, and 1-Beach have a high reliability.

Then, a method for fabricating elements (an example element 2 and acomparative example element 2) to evaluate crosstalk is described.

(Method for Fabricating Example Element 2)

To evaluate crosstalk, a passive matrix panel whose resolution was 326ppi was fabricated. In this panel, pixels for R, G, and B were arrangedin a stripe. The pixel size was 78 μm×78 μm. The size of a subpixel (ineach pixel for R, G, or B) was 26 μm×78 μm. The aperture ratio was65.7%.

Substances used in the example element 2 and the comparative exampleelement 2 are shown below. For the materials also used in the exampleelement 1 and the comparative example element 1, the above structuralformulae are referred to.

In each pixel, as an anode 100, an aluminum-nickel-lanthanum alloy filmand a titanium film were sequentially deposited by a sputtering method.The thickness of the aluminum-nickel-lanthanum alloy film was 200 nm andthe thickness of the titanium film was 6 nm.

Then, indium tin oxide containing silicon oxide (ITSO) was depositedover the anode 100 by a sputtering method, whereby a first conductivelayer 107 was formed. In order to have a microcavity effect in the pixelfor R, the pixel for G, and the pixel for B of the example element 2,the thickness of the first conductive layer 107 was set to 80 nm in thepixel for R, the thickness of the first conductive layer 107 was set to40 nm in the pixel for G, and the first conductive layer 107 was notprovided in the pixel for B.

Next, in pretreatment for forming the light-emitting element over thesubstrate, a surface of the substrate was washed with water and baked at200° C. for 1 hour, and then UV ozone treatment was performed for 370seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus whose pressure was reduced to about 10⁻⁴ Pa, vacuum baking wasperformed at 170° C. in a heating chamber of the vacuum evaporationapparatus for 30 minutes, and then the substrate was cooled down forabout 30 minutes.

Then, the substrate over which the anode 100 was formed was fixed to asubstrate holder provided in the vacuum evaporation apparatus so thatthe surface over which the anode 100 was formed faced downward. Thepressure in the vacuum evaporation apparatus was reduced to about 10⁻⁴Pa. After that, on the anode 100,9-pheny-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA) represented by the above structural formula (xiii) andmolybdenum(VI) oxide were deposited by co-evaporation by an evaporationmethod using resistance heating, whereby a first hole-injection layer111_1 was formed. The thickness was set to 13 nm. The weight ratio ofPCzPA to molybdenum oxide was adjusted to 1:0.5 (=PCzPA:molybdenumoxide). Note that the co-evaporation method refers to an evaporationmethod in which evaporation is carried out from a plurality ofevaporation sources at the same time in one treatment chamber.

Next, PCzPA was deposited to a thickness of 20 nm on the firsthole-injection layer 111_1, whereby a first hole-transport layer 112_1was formed.

Then, on the first hole-transport layer 112_1,9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (II) andN,N-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation:1,6mMemFLPAPrn) represented by the above structuralformula (iii) were deposited by co-evaporation to a thickness of 30 nmso that the weight ratio of CzPA to 1,6mMemFLPAPrn was 1:0.05 (=CzPA:1,6mMemFLPAPrn), whereby a first light-emitting layer 113_1 was formed.

After that, CzPA was deposited to a thickness of 5 nm, and2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBPhen) represented by the above structural formula (Iv) was depositedto a thickness of 15 nm, whereby a first electron-transport layer 114_1was formed. Components from the first hole-injection layer 111_1 to thefirst electron-transport layer 114_1 are collectively referred to as afirst light-emitting unit 102_1.

A charge generation layer 103 was formed on the first light-emittingunit 102_1. The charge generation layer 103 was formed in the followingmanner. First, as part of an electron-injection buffer region 105, alithium layer was formed by using lithium oxide. The thickness thereofwas 0.1 nm. Then, as an electron-relay region, copper phthalocyanine(abbreviation: CuPC) represented by the above structural formula (v) wasdeposited to a thickness of 2 nm. After that, as a charge generationregion 104, PCzPA and molybdenum(VI) oxide were deposited byco-evaporation to a thickness of 13 nm. The weight ratio of PCzPA tomolybdenum oxide was adjusted to 1:0.5 (=DBT3P-II:molybdenum oxide).

Next, on the charge generation layer 103,4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)represented by the above structural formula (vii) was deposited to athickness of 20 nm as a second hole-transport layer 112_2.

Then, 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) represented by the above structuralformula (viii),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB) represented by the above structural formula (ix),andbis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)) represented by the above structuralformula (x) were deposited by co-evaporation to a thickness of 20 nm sothat the weight ratio of 2mDBTBPDBq-II to PCBNBB and Ir(tBuppm)₂(acac)was 0.7:0.3:0.06 (=2mDBTBPDBq-II:PCBNBB:Ir(tBuppm)₂(acac)). Then,2mDBTBPDBq-II and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm))represented by the structural formula (xiv) were deposited byco-evaporation to a thickness of 20 nm so that the weight ratio of2mDBTBPDBq-II to Ir(tppr)₂(dpm) was 1:0.06(=2mDBTBPDBq-II:Ir(tppr)₂(dpm)), whereby a second light-emitting layer113_2 was formed.

After that, on the second light-emitting layer 113_2, 2mDBTBPDBq-II wasdeposited to a thickness of 15 nm, and bathophenanthroline(abbreviation: BPhen) represented by the structural formula (xii) wasdeposited to a thickness of 15 nm, whereby a second electron-transportlayer 114_2 was formed.

After the second electron-transport layer 114_2 was formed, lithiumfluoride (LiF) was deposited by evaporation to a thickness of 1 nm,whereby an electron-injection layer 115_2 was formed. Lastly, silver wasdeposited to a thickness of 15 nm and then PCzPA was deposited to athickness of 70 nm to form the cathode 101. Thus, the example element 2was fabricated. Components from the second hole-transport layer 112_2 tothe electron-injection layer 115_2 corresponds to a secondlight-emitting unit 102_2.

Note that in the above evaporation steps, evaporation was performed by aresistance-heating method.

Now, a method for fabricating the comparative light-emitting element(the comparative example element 2) will be described.

(Method for Fabricating the Comparative Example Element 2)

The comparative example element 2 was fabricated by usingbathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (xii) for the first electron-transport layer 114_1instead of NBPhen that was used in the example element 2. Othercomponents were formed in a manner similar to those of the exampleelement 2.

The example element 2 and the comparative example element 2 were eachsealed using a glass substrate provided with a color filter in a glovebox containing a nitrogen atmosphere so as not to be exposed to the air(specifically, a sealant was applied onto an outer edge of the elementand UV treatment and heat treatment at 80° C. for 1 hour were performedat the time of sealing). Then, characteristics of these light-emittingelements were measured. Note that the measurements were performed atroom temperature (in an atmosphere kept at 25° C.).

FIG. 12 shows the results of examining crosstalk. In FIG. 12, enlargedphotographs of display devices that were formed by using the comparativeexample element 2 and the example element 2 are shown. A photograph inwhich only red pixels emit light, a photograph in which only greenpixels emit light, and a photograph in which only blue pixels emit lightare shown from the top to the bottom.

It was found that in the display device fabricated using the comparativeexample element 2, pixels adjacent to the pixels which emit light alsosomewhat emit light. On the other hand, in the display device fabricatedusing the example element 2, light emission of pixels adjacent to thepixels which emit light is weak. In addition, in the display deviceusing the example element 2, there are a small number of lines of pixelswhich can be recognized on the left side of the leftmost pixels thatemit light.

As described above, in the light-emitting element according to oneembodiment of the present invention, crosstalk between pixels can beeffectively suppressed. In particular, in a high-definition displaydevice in which the distance between pixels is less than or equal to 80μm and the distance between subpixels is less than or equal to 30 μm,the light-emitting element according to one embodiment of the presentinvention is effective to suppress crosstalk between pixels.

This application is based on Japanese Patent Application serial no.2013-166867 filed with Japan Patent Office on Aug. 9, 2013, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting element comprising: a firstelectrode; an EL layer over the first electrode; and a second electrodeover the EL layer, wherein the EL layer comprises a first light-emittingunit, a first layer, a first charge generation layer, a secondlight-emitting unit, a second layer, and a second charge generationlayer, wherein the first layer is provided between the firstlight-emitting unit and the first charge generation layer, wherein thesecond layer is provided between the second light-emitting unit and thesecond charge generation layer, and wherein the first layer and thesecond layer comprise2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline.
 2. Thelight-emitting element according to claim 1, wherein the first chargegeneration layer comprises at least a charge generation region and anelectron-injection buffer region.
 3. The light-emitting elementaccording to claim 2, wherein an electron-relay region is providedbetween the charge generation region and the electron-injection bufferregion.
 4. The light-emitting element according to claim 2, wherein theelectron-injection buffer region comprises an alkali metal.
 5. Thelight-emitting element according to claim 1, wherein the EL layercomprises a layer containing a condensed heteroaromatic compound,wherein the layer containing a condensed heteroaromatic compoundcomprises iridium and a compound which comprises two nitrogen atoms inone condensed ring, and wherein the layer containing a condensedheteroaromatic compound is in contact with the first layer.
 6. Thelight-emitting element according to claim 5, wherein the iridium iscontained in part of the layer containing a condensed heteroaromaticcompound and not contained in a region in contact with the first layer.7. A light-emitting device comprising the light-emitting elementaccording claim 1 and a unit configured to control the light-emittingelement.
 8. A display device comprising the light-emitting elementaccording to claim 1 in a display portion and a unit configured tocontrol the light-emitting element.
 9. A lighting device comprising thelight-emitting element according to claim 1 in a lighting portion and aunit configured to control the light-emitting element.
 10. Alight-emitting element comprising: a first electrode; an EL layer overthe first electrode, the EL layer comprising: a first light-emittingunit over the first electrode; a first layer over the firstlight-emitting unit; and a first charge generation layer over and incontact with the first layer, and a second electrode, wherein the firstlayer comprises2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline.
 11. Thelight-emitting element according to claim 10, wherein the first chargegeneration layer comprises at least a charge generation region and anelectron-injection buffer region.
 12. The light-emitting elementaccording to claim 11, wherein an electron-relay region is providedbetween the charge generation region and the electron-injection bufferregion.
 13. The light-emitting element according to claim 11, whereinthe electron-injection buffer region comprises an alkali metal.
 14. Thelight-emitting element according to claim 10, wherein the EL layercomprises a layer containing a condensed heteroaromatic compound,wherein the layer containing a condensed heteroaromatic compoundcomprises iridium and a compound which comprises two nitrogen atoms inone condensed ring, and wherein the layer containing a condensedheteroaromatic compound is in contact with the first layer.
 15. Thelight-emitting element according to claim 14, wherein the iridium iscontained in part of the layer containing a condensed heteroaromaticcompound and not contained in a region in contact with the first layer.16. A light-emitting device comprising the light-emitting elementaccording claim 10 and a unit configured to control the light-emittingelement.
 17. A display device comprising the light-emitting elementaccording to claim 10 in a display portion and a unit configured tocontrol the light-emitting element.
 18. A lighting device comprising thelight-emitting element according to claim 10 in a lighting portion and aunit configured to control the light-emitting element.
 19. Alight-emitting element comprising: a first electrode; an EL layer overthe first electrode, the EL layer comprising: a hole-injection layerover the first electrode; a hole-transport layer over the hole-injectionlayer; a light-emitting layer over the hole-transport layer; anelectron-transport layer over the light-emitting layer, theelectron-transport layer comprising a first layer; and a first chargegeneration layer over the electron-transport layer; and a secondelectrode over the first charge generation layer, wherein the firstlayer comprises2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline.
 20. Thelight-emitting element according to claim 19, wherein the first chargegeneration layer comprises at least a charge generation region and anelectron-injection buffer region.
 21. The light-emitting elementaccording to claim 20, wherein an electron-relay region is providedbetween the charge generation region and the electron-injection bufferregion.
 22. The light-emitting element according to claim 20, whereinthe electron-injection buffer region comprises an alkali metal.
 23. Thelight-emitting element according to claim 19, wherein the EL layercomprises a layer containing a condensed heteroaromatic compound,wherein the layer containing a condensed heteroaromatic compoundcomprises iridium and a compound which comprises two nitrogen atoms inone condensed ring, and wherein the layer containing a condensedheteroaromatic compound is in contact with the first layer.
 24. Thelight-emitting element according to claim 23, wherein the iridium iscontained in part of the layer containing a condensed heteroaromaticcompound and not contained in a region in contact with the first layer.25. A light-emitting device comprising the light-emitting elementaccording claim 19 and a unit configured to control the light-emittingelement.
 26. A display device comprising the light-emitting elementaccording to claim 19 in a display portion and a unit configured tocontrol the light-emitting element.
 27. A lighting device comprising thelight-emitting element according to claim 19 in a lighting portion and aunit configured to control the light-emitting element.